1. Field of the Invention
The present invention relates to vehicle lamps suitable for use as car front lamps, and particularly to a vehicle lamp using a discharge bulb as a light source in which influence of electromagnetic waves is prevented from acting on the lamp.
2. Background Art
Recently, the idea of using a discharge bulb as a light source for a car lamp has been considered. The reason is that a discharge bulb is excellent in luminous efficiency and color rendering property, and has a long life time. A lamp of this kind, however, requires a high voltage for generating a discharge in the discharge bulb. Accordingly, it is necessary to provide a turn-on circuit on the lamp to raise the voltage of the car battery to a required high value. Further, since a high voltage is generated on the secondary side of the turn-on circuit, electromagnetic waves are radiated outside with the generation of the high voltage and the electromagnetic waves have an influence, as noise, on various car electronic apparatuses to thereby disturb the normal operation of these apparatuses. For example, noise is generated in a radio receiver or noise is mixed into a signal system of a microcomputer mounted on a car, that is, a so-called EMI (electromagnetic interference) is generated.
Further, electromagnetic waves are generated also in the discharge bulb to which the foregoing high voltage is applied and the foregoing EMI is generated by the electromagnetic waves radiated from the discharge bulb. Therefore, for example, JP-A-5-101703 discloses a vehicle lamp in which a shielding member is provided along an inner surface of a lamp body so as to shield a circumference of a discharge bulb and/or a reflector. According to this technique, the radiation of electromagnetic waves to the circumference of the discharge bulb is suppressed through the shielding member to thereby cope with EMI.
This conventional technique is effective in suppression of radiation of electromagnetic waves toward the circumference of the discharge bulb. However, it is necessary to provide a shielding member throughout the circumference of a reflector provided in the lamp body. Therefore, in order to create the space for arranging the shielding member, the size of the lamp body must be increased. Consequently, the conventional technique is not suitable for forming a small sized lamp. An additional complication results from the fact that the reflector is tilted in the up/down and right/left directions in order to adjust the optical axis (i.e., to aim the light). Since the shielding member is provided to cover the region in front of the reflector, which moves relatively large distances at the time of the adjustment of aiming, it is necessary to provide correspondingly large distances between the reflector and the shielding member for the purpose of preventing interference between the reflector and the shielding member. Consequently, the lamp body is necessarily large in size.
Further, in this conventional technique, it is difficult to suppress radiation of electromagnetic waves from a cap of the discharge bulb, that is, a bulb socket portion, although the technique is effective in suppression of radiation of electromagnetic waves from the portion of the discharge bulb enclosed by the shielding member. There is also a fear that electromagnetic waves from the bulb socket portion are radiated outside through the lamp body which is made of resin. In this case, although such electromagnetic waves can be suppressed if the lamp body is made of a metal material, the total weight of the lamp increases. Further, it is difficult to suppress electromagnetic waves radiated from the gap between the shielding member and the reflector to the front side of the lamp.